A GP practice run by a doctor who has been of one of the most prominent supporters of Andrew Lansley's health reforms de-registered elderly and disabled care home patients to save money, an NHS investigation has found.

According to documents obtained by a freedom of information request, the NHS launched an investigation into Churchill medical practice in Kingston last year after complaints that it had let go of 48 patients who required high levels of care. Local doctors complained as they had been expected to take on the vulnerable and costly patients – some with Alzheimer's disease – at short notice.

Churchill's senior partner was Charles Alessi, now chair of the National Association of Primary Care, who has written in the Sun and appeared on television backing the coalition's health reforms. According to the documents, the practice claimed it was forced to drop the patients because they had to cut staff after NHS funding dried up in March last year.

NHS South-west London found that Churchill was in breach of its "contractual obligations to patients" by removing the patients and that it had done so "predominantly for financial reasons". The NHS issued a breach of contract notice. Three infringements would mean that Churchill's GPs lost the right to practice.

In the documents, an unnamed NHS director leading the probe said: "I could draw no conclusion other than that you subsequently selected 48 vulnerable people for removal from your list of patients because of their demands on your practice's services and this by virtue of their age, medical condition or level of disability."

Local GPs told the Surrey Comet, which obtained the documents, that "patient care must not become a pawn in these processes".

The case became a cause celebre in the NHS because critics of the health reforms said that giving GPs power over budgets would see family doctors attempt to save money by dodging their responsibility to patients – by excluding the most sick and expensive.

When contacted, Alessi, who left Churchill this year to take his role at NAPC, said that the local primary care trust had "changed the contract and cut the money. We felt we could not deliver the care required any more and patient safety was our concern. So the decision was taken. I think that the contracts in the new NHS will be much better than these."

Labour's health spokesman, Andy Burnham, who has long warned of the possible consequences to patient care of the reforms, said: "It is simply unacceptable for vulnerable patients to be treated in this way. One of our biggest concerns is that the new system weakens accountability in the NHS and makes situations like this more likely as the public are less able to challenge it.

"The government must ensure that the full implications of these findings are communicated to all clinical commissioning groups to ensure there's no repeat of this outrageous practice."

In a statement, Churchill said it was "disappointed" with the NHS conclusions. "The decisions taken by the practice were all taken in good faith after the practice made attempts to communicate and get assent to the actions proposed. These events took place after a protracted and polarised contractual dispute between the practice and the PCT, and at a time of transition … The practice believes that these were significant contributory factors to events as they unfolded."

A spokesperson for NHS South-west London said: "We've issued a formal notice to the practice which states that they can't repeat the activities that have put them in breach of contract, and we continue to monitor the practice closely. We took action to ensure that all of the affected patients from Kingston Care Home were allocated a new local GP as soon as we were alerted to this issue, to ensure that their health needs continued to be met."